Low pressure controlled discharge device



Q Souacz .BQ H 29 Oct. 5,1943. c. G. SMITH" I Y 2,330,349

Low PRESSURE CONTROLLEDVDI'SCHARGE DEVICE Fi'led Aug. 27, 1940 v y '3 Sheets-Sheet i I V Tml.

I A.C., I v

. 'lN'yEN o CHARLES ,sMlTH,

ATTY,

- Oct. 5, 1943; Q 5 2,330,849

LOW PRESSURE CONTROLLED DISCHARGE DEVICE Filed Aug. 27, 1940 3 Sheets-Sheet 2 |NVENTR. CHARLES G. SMITH,

BY v

Oct. 5, 1943. c. 6. SMITH LOW PRESSURE.CONTROLLED DISCHARGE DEVICE Filed Aug 27, 1940 s Sheets-Sheet 5 FIGS.

[ TIMING SWITCH U INVENTOR. CHAR LES. G. SMIT H,

Patented Oct. 5, 1943 2,330,849 I LOW ranssmm conraonmn msoimacn nsvron Charles G. Smith, Medl'ord, Mass., assignor to Raytheon Manufacturing Company, Newton,

Mass., a corporation of Delaware Application August 27, 1940, Serial No. 354,387 23 Claims. (Cl. 250-275) This invention relates to a controlled electrical discharge device of the gaseous type which operates at relatively low gas or vapor pressures and conducts current of high power with relatively low losses.

This invention is based upon certain discovrents of hundreds of amperes through mercury vapor at pressures below on micron. I have also caused such discharges to pass through gaseous atmospheres contained within a ring entirely made of metal, except for one or more insulating sections which prevent the metal from acting as a short circuit. I have further shown that at excessively low pressures of the order of 1(l mm. and even lower pressures, large ring currents can be passed, and the resultant ionization can be used to substantiallycompletely neutralize space charge in the region between a thermionic cathode and an anode exposed in the discharge. I have further observed that cathodes at temperatures below the usual thermionic emission range, when exposed to such a discharge, may be employed as cathodes supplying many amperes of current and having said current under complete control of the discharge.

An object of this invention is to utilize the foregoing discoveries for the purpose of making an eflicient, controllable, unidirectionally conducting device.

Another object is to provide such a device capable of rectifying large amperages and voltages.

A further object is to produce such a device in which the conduction of current is under complete control of a relatively small controlling infiuence.

The foregoing and other objects of my invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a cross-section of my novel tube together with a diagrammatic representation of a typical circuit with which it may be used;

Fig. 2 is a cross-section taken along line 22 of Fig. 1; and

Fig. 3 is a showing similar to Fig. 1 of an additional embodimentof my invention, the tube, however, not being shown in section.

V In the arrangement illustrated in Figs. 1 and v 2, the tube consists of a metal torus I made of some suitable material, such as stainless or chrome steel or aluminum. The metal of the torus is interrupted at 2, and a ring of insulation 3 sealed to. a pair of flanges 4v which are welded to the torus I is utilized to complete the torus and to make it hermetically tight. A side tube 5 extends from one side of the torus I, and contains a small quantity 8 of vaporizable material, such as mercury or caesium. Other vaporizable materials, such as the other alkali metals, may also be used. The use of caesium or potassium may be made particularly effective inasmuch as the walls of the torus I can be made to reflect substantially all of the radiations emitted from ionized caesium or potassium vapor, and thus. greatly increase the efflciency of the device. The side tube 5 may be maintained at a constant predetermined temperature by immersing it in a constant temperature bath or the like so as to maintain the pressure within the torus l at a predetermined value. This pressure is preferably of the order of one micronof mercury or less. For example, in the case of mercury, the

' temperature of the side tube 5 may be about 5 C.

or higher. In the case of caesium, the temperature may be about 0., while in the case of potassium, the temperature may be about C. Of course it is to be understood that higher values of temperature, and in some instances even. lower values of temperature, may be utilized. One or more grids I may be interposed across the side tube 5 in order to prevent the discharge within the torus I from extending through to the vaporizable material 6, and producing an excessive vaporization thereof.

I have found that a discharge may be readily started through gases at the low pressures mentioned if a number of ions are introduced into the discharge space. Such ions may be supplied by providing a filament 8 adapted to be heated to a temperature of thermionic emission. The

filament- 8 may be sealed through a glass stem III, which in turn is sealed to the outer end of a tubular extension II formed on the torus I. The filament 8 may be located well within the extension formed by the tubular member II and the stem I0 and yet cause a suificient number of ions to pass out into the main body of the torus I forthe desired purpose.

An anode I2 formed by a reentrant metal cup is insulatingly sealed to a tubular extension I3 by means of an insulating sealing ring I4, preferably of glass. A lead I5 is secured to the outer sideoi'theanode I2 so astoprovideanelectrlcal connection therein. A grid I9 is preferably provided across the opening to the tubular extension I3, the grid I9 being electrically connected to and supported by the torus I. The torus I, which in the present instance is to serve as the cathode, is provided with an electrical connecthree to seven inches for the diameter of saidcentral opening. -In addition the cross-section of the gaseous path determined by the crosssection of the tubular portion of the torus should be relatively large. In certain cases I have utilized values of from one to six inches for the diameter of said cross-section. Of course these dimensions may be departed from considerably.

Electrodeless discharge currents are induced in the torus I by means of a suitable transformer I8 comprising a magnetic core preferably made of iron of high magnetic permeability. The core is provided with a central leg I9 of maximum size to conveniently pass through the central opening in the torus I. The core is also provided with a pair of outer legs 20. The lower ends of the legs I9 and 20 are joined by a lower leg I9. The upper ends of the legs I9 and 20 provide pole faces 20. These pole faces are ground ofi flat so as to provide as smooth a surface as practicable without the presence of projecting portions, such as burrs and the like. In addition it is also preferable to'paint the faces of the pole pieces 20 with a thin insulating varnish. A top leg I8 likewise ground flat ad- Jacent the pole pieces 20' is laid across the tops or the legs I9 and 20 so as to complete the magnetic circuit of the transformer. The leg I8 may beretained in place by any suitable fastening means which preserves the slight air gap provided at the pole pieces 20' by the above construction. At the upper and lower ends of each of the legs I9 and 20 is provided an energizing coil 2I, resulting in a total of six such coils in the arrangement of Figs. 1 and 2. The coils 2I are adapted to be supplied with energizing currents of frequencies of the order of 1000 to 2000 cycles. In devices of this kind the presence of transverse fields intersecting the gaseous discharge path are-undesirable inasmuch as such fields interfere with the free passage of the discharge. The symmetrical arrangement of the transformer I8 and the exciting coils 2I reduce leakage fluxes to aminimum, and substantially prevent the presence of transverse magnetic fields in the gaseous discharge space. The upper coils 2i are placed closely adjacent the air gaps 20, whereby leakage fluxes from these air gaps are likewise minimized.

The arrangement described above may be connected in any suitable circuit, such as shown,

' for example, in Fig. 1. In this circuit the filament 8 is provided with heating current from a heating transformer 22. The filament 8 is connected through a current-limiting resistance 23 and a source of potential, such as a battery 24, to the connection II of the torus I. In this way an ionizing discharge may be maintained beassasco tween the torus I and the filament 9 for the a purpose of generating ions to facilitate startins of the main discharge. A relatively small number of positive ions isneeded for this purpose, and therefore only a few milliamperes passing between the filament 9 andthe torus I are usually suillcient for starting said main discharge. The current to be rectified is applied to the tube fromapower transformer 29 having a primary winding 29 adapted to be connected to a suitable source of alternating current, and a secondary winding 21 connected in series with the load 28 between the cathode I and the anode I2. A suitable source 29 of alternating current of the desired frequency, for example 1000 to 2000- cycles, is connected to the energizing coils 2I in series with the control switch 29'. The current output of the source 29 may be modulated from a pair of leads 39 energized from a source of alternating current of the same frequency and bearing a definite phase relationship with respect to the alternating current energizing the primary winding 26 of the transformer 25. The modulation and phase relationship are preferably such that current is supplied to the coils 2| when the anode I2 is positive with respect to the cathode I, and such energizing currents are stopped during the time that the anode I2 is negative with respect to the cathode I. The electromotive force around the closed gaseous discharge loop maybe relatively small, of the order of 15 volts more or less.

When the system is energized, electrons from the filament 8 cause ionization throughout the interior of the torus. When the switch'29' is closed, an intense ring discharge is initiated around the closed gaseous discharge loop. In absence of an auxiliary supply of ions as described above, the starting of such a discharge at the low pressures described would be extremely diiiicult.

Under the conditions of the intense electrodeless' discharge, a large amount of current may be passed between the torus I acting as a cathode and the anode I2 representing a' large emission of current carriers from the cathode I. A large part of this emission is probably caused by large numbers of positive ions arriving at the walls oi the torus I where they recombine with electrons. Some of the emission is undoubtedly due to causes in addition to such positive ion collection. The current emission from the interior walls of the torus I can readily be made 10 milliamper'es per square centimeter and even greater in accordance with observations made on such tubes. In order that the current passing between the oathode I and the anode I2 be 200 amperes, the internal area of the torus I need only be about 2x10 square centimeters.

Under the above conditions, age of the secondary winding 21 makes the anode I2 positive with respect to the cathode I, substantially 200 amperes of current may bedrawn to said anode. When, however, the voltage becomes negative, the inducing currents to the coils 2I are cut ofi, and therefore substantially no current can be drawn between the anode I2 and cathode I. This is true even if high voltages are impressed between the electrodes. Such voltages may be of the order of 10,000 volts, for example. The conduction of current is thus under complete control of the source 29. If, for example, it is desired to stop all flow of current to the load 29, it is merely necessary to open the switch 29'. The tube, therefore, acts as a very whenever the voltrespectively.

of course it is to be understood that this inveneffective rectifier for supplying direct current to the load 28.

The voltage drop during the period of current flow between the anode I2 and the cathode I is relatively small, being of the order of five volts more or less in the case of mercury vapor. The rectifier illustrated, therefore, is very eflicient, due to the low drop which it is thus possible to secure. As previously indicated in the case of the alkali metals, by making the interior surfaces of the torus I reflecting to the radiations generated in said vapors, the drop through the tube may be made relatively smaller than in the case of mercury, and therefore the efilciency may be relatively greater.

Although the arrangement has been described in connection with a magnetic core transformer, in some instances with the proper selection of frequency and other constants, the iron core can be eliminated and merely an air core coupling made between theexciting coils and the torus I.

Since-the conduction of current between the cathode I and the anode I2 is under complete control of the excitation source 29, the tube may be made for other purposes than rectification. For example, if a direct current power source is connected between the cathode I and the anode I2 in a direction so as to make the anode I2 positive, conduction of direct current through the tube will be under complete control of the switch 29' so that by closing said switch, direct current is permitted to flow, while openingof the switch will cut off flow of direct current. In this way by closing and opening the switch 29' at a predetermined frequency, the direct current can be periodically interrupted, thus causing the tube to function as an inverter.

The invention can also be employed to control alternating current instead of direct current. Such an arrangement is illustrated in Fig. 3 wherein identical reference numerals are applied where the elements are identical with those of Figs. 1 and 2. In Fig. 3 the tube, instead of having a single interruption in the torus, is provided with two such interruptions at diametrically opposite points, dividing the torus into two halves 30 and 3|. These halves are provided with external electrical connections 32 and 33, The side tube 5 and the extension I I containing the ionizing filament are employed. However, the anode of Fig. 1 is omitted. The tube of Fig. 3 is supplied with power from a power transformer 34 having a primary winding 35 adapted to be connected to a suitable source of alternating current, and a secondary winding 36. One end of said secondary winding is connected to the half 30, while the other end is connected through a suitable load 31 to the other half 3|. The switch 29' of Fig. 1 may be replaced by a timing switch 38 which may be operated in accordance with a predetermined time sequence. When the switch 38 is in its closed position, alternating current will pass between the two halves 30 and 3I,'while in the open position of said switch, flow of currentbetween said halves will be stopped. In this way alternating current will be supplied to the load 31 in accordance with the time sequence of operation of the switch 38. The load 31 may be, for example, a resistance welding load in which case the timing switch 38 is preferably operated in synchronism with the alternating current supply so as to furnish a predetermined number of cycles to the load 31 for each operation of the switch 38.

tion is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An electrical discharge device comprising an envelope containing an ionizable gaseous atmosphere, means for producing an electrodeless discharge in said atmosphere, a cathode surface of the type from which emission is dependent on the presence of an ionizing discharge, said cathode surface substantially surrounding said discharge, and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surface to substantially cease upon stoppage of said electrodeless discharge.

2. An electrical discharge device comprising an envelope containing an ionizabl gaseous atmosphere, means for producing an electrodeless discharge in said atmosphere, means for introducing ions for facilitating starting of said electrodeless discharge, a cathode surface of the type from which emission is dependent on the presence of an ionizing discharge, and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmosphere being sufficiently low to cause emission from said cath ode surface to substantially cease upon stoppage of said electrodeless discharge.

3. An electrical discharge device comprising an envelope containing an ionizable gaseous atmosphere at a pressure of the order of one micron or less, means for producing an electrodeless discharge in said atmosphere, a cathode surface of the type from which emission is dependent on the presence of an ionizing discharge, and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmospherebeing sufficiently low to cause emission from said cathode surface to substantially cease upon stoppage of said electrodeless discharge.

4. An electrical discharge device comprising an envelope containing an ionizable gaseous atmosphere at a pressure of the order of one micron or less, means for producing an electrodeless discharge in said atmosphere, means for introducing ions for facilitating starting of said electrodeless discharge, a cathode surface of the type from which emission is dependent on the presence of an ionizing discharge, and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmosphere being suificiently low to cause emission from said cathode surface to substantially cease upon stoppage of said electrodeless discharge.

5. An electrical discharge device comprising a ring-shaped envelope providing a closed ringshaped discharge path and containing an ionizable gaseous atmosphere, means .for producing a ring discharge in said atmosphere, a cathode surface of the type from which emission is dependent 0n the presence of an ionizing discharge, and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmosphere being sufliciently low to cause emission from said cathode surface to substantially cease upon stoppage of said ring discharge.

6. An electrical discharge devic comprising an envelope containing an ionizable gaseous atmosphere, electromagnetic means for inducing an electrodeless discharge in said atmosphere, means for introducing ions for facilitating starting of said electrodeless discharge, and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surface to substantially cease upon stoppage of said el'ectrodeless discharge.

- '7. An electrical discharge device comprising a ring-shaped envelope providing a closed ringshapeddischarge path and containing an ionizable. gaseous atmosphere at a pressure of the order of one micron or less, a cathode surface of the type from which emission is dependent on the: presence of an ionizing discharge, electromagnetic means for inducing a ring discharge in said atmosphere, and means for introducing ions for facilitating starting of said ring discharge. 8. An electrical discharge device comprising a ring-shaped envelope providing a closed ringshaped discharge path and containing an ionizable gaseous atmosphere at a pressure of the or- -der of one micron or less, and electromagnetic means producing flux interlinking said ring for inducing a ring discharge in said atmosphere, said electromagnetic means being arranged to substantially prevent magnetic fields transverse to the path of said discharge.

9. Anelectrical discharge device comprising a ring-shaped envelope providing a closed ringshaped discharge path and containing an ionizable gaseous atmosphere at a pressure of the order of one micron or less, electromagnetic means producing flux interlinking said ring for inducing a ring discharge in said atmosphere. said electromagnetic means being arranged to substantially prevent magnetic fields transverse to the path of said discharge, and means for introducing ions for facilitating starting of said electrodeless discharge.

10. An electrical discharge device comprising a metal ring-shaped envelope providing a closed ring-shaped discharge path and containing an ionizable gaseous atmosphere, the interior surface of said envelope being adapted to function as a cathode, and an electrode surface adapted to operate as an anode for said cathode surface, additional means for producing an ionizing discharge in said atmosphere, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surface to substantially cease upon stoppage of said discharge.

11. An electrical discharge device comprising a metal ring-shaped envelope providing a closed ring-shaped discharge path and containing an ionizable gaseous atmosphere, said metal ring having an insulating interruption for preventing short-circuit of said gaseous atmosphere, the interior surface of said envelope being adapted to function as a cathode, and an electrode surface adapted to operate as an anode for said cathode surface, additional means for producing an'ionizing discharge in said atmosphere, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surface to substantially cease' upon stoppage of said discharge.

12. An electrical discharge device comprising a metal ring-shaped envelope providing a closed ring-shaped discharge path and containing an ionizable gaseous atmosphere, said metal ring being divided into two parts insulated from each other, the interior surfaces of said parts being adapted to function as cathode surfaces, additional means for producing an ionizing discharge in said atmosphere, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surfaces to substantially cease upon stoppage of. said discharge.

13. An electrical discharge device'comprisinz an envelope containing alkali metal vapor, the interior walls of said envelope having a surface which reflects most of the radiations emitted from I said vapor during operation, means for producing an electrodeless discharge in said atmosphere, a cathode surface of the type from which emission is dependent on the presence of an ionizing discharge, and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmosphere being sunlciently low to cause emission from said cathode surface to substantially cease upon stoppage of said electrodeless discharge.

14. 'An electrical discharge device comprising a metal envelope containing an ionizable gaseous atmosphere, the interior surface of said envelope being adapted to function as a cathode. and an electrode surface adapted to operate as an anode for said cathode surface, additional means for producing an ionizing discharge in said atmosphere, the pressure of said atmosphere being sufflciently low to cause emission from said cathode surface to substantially cease upon stoppage of said discharge.

15. An electrical discharge device comprising a 7 metal envelope containing an ionizable gaseous atmosphere, said metal envelope having an insulating interruption for preventing short-circuit of said gaseous atmosphere, the interior surface of said envelope being adapted to function as a cathode, and an electrode surface adapted to operate as an anode for said-cathode surface, additional means for producing an ionizing discharge in said atmosphere, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surface to substantially cease upon stoppage of said discharge.

16. An electrical discharge device comprising a metal envelope containing an ionizable gaseous atmosphere, said metal envelope being divided into two parts insulated from each other, the interior surfaces of said parts being adapted to function as cathode surfaces, additional means for producing an ionizing discharge in said atmosphere, the pressure of said atmosphere being suillciently low to cause emission from said cathode surfaces to substantially cease upon stoppage of said discharge.

17. An electrical discharg device comprisin an envelope having a conductive interior wall surface and containing an ionizable gaseous atmosphere, said conductive interior wall surface being adapted to function as a cathode, and an electrode surface'adapted to operate as an anode for said cathode surface, additional means for producing an ionizing discharge in said atmosphere, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surface to substantially cease upon stoppage of said discharge.

18. An electrical discharge device comprising a ring-shaped envelope providing a closed ringshaped discharge path and containing an ionizable gaseous atmosphere, and electromagnetic means producing flux interlinking said ring for inducing a ring discharge in said atmosphere, said electromagnetic means being arranged to substantially prevent magnetic fields transverse to the path of said discharge.

19. An electrical discharge device comprising an envelope containing an ionizable gaseous atmosphere, means for producing a discharge in c said atmosphere, a'cathode surface of the type from which emission is dependent on the presence 01' an ionizing discharge, said cathode surface substantially surrounding said discharge,

and an electrode surface adapted to operate as an anode for said cathode surface, the pressure of said atmosphere being sufficiently low to cause emission from said cathode surface to substantially cease upon stoppage of said discharge.

20. An electrical discharge device comprising an envelope containing an ionizable gaseous atmosphere, means for producing an electrodeless.

21. An electrical discharge. device comprising ,an ionizable atmosphere, means for producing a discharge in said atmosphere, and means surrounding said discharge, said last-named means having an internal surface which reflects most of the radiations emitted from said atmosphere during operation.

said discharge.

22. An electrical discharge device comprising an alkali vapor, means for producing a discharge in said vapor, and means surrounding said discharge, said last-named means having an internal surface which reflects most of the radiations emitted from said vapor during operation.

23. An electrical discharge device comprising an envelope providing a closed ring-shaped discharge path and containin an ionizable gaseous atmosphere, and electromagnetic means producing flux interlinking said ring for inducing a ring discharge in said atmosphere, said electrom gnetic means being arranged to substantially preventmagnetic fields transverse to the path of CHARlZ-ES G. smrrny 

